Plastics, particularly polystyrene, are used in the building industry as sheet insulation. Lately, major building projects have used the polystyrene, subject to certain sealing and decorative finishes, as a finished interior or exterior wall. Dryvit Systems, Inc., under the trade name "Dryvit," is an example of a polystyrene product used in such manner.
The polystyrene is usually furnished in 4'.times.8' sheets of selected thickness. It must be cut and fitted as any building material which must conform to a finite space. When in place, the exposed surface of the polystyrene at best conforms to the subsurface to which it is attached; therefore, the polystyrene requires surface preparation such as planing and trimming before the final finish can be applied. This planing and trimming is only feasible after the panels are permanently fixed in place; thus, any tool which performs the required planing and trimming must be hand held, light, and portable enough for use by one workman.
Heretofore, the typical tool available which was light, portable, hand held, and capable of suitably shaping a polystyrene block was a sanding block and coarse grit sandpaper. Such a process was slow, expensive, and often left a rough surface to receive the final finish. The present invention provides a smooth sheared surface quickly at minimal expense. In addition, the tool is versatile enough to be used as a fitting tool for initial installation of the polystyrene blocks and it can even be used to make decorative cuts.
In accordance with the present invention, an external power source and earth ground are utilized such as are commonly found in household outlets. An electrical power unit converts incoming electrical energy to a safe, low voltage, limited amperage output. Output flows by means of one leg of a power cord to a safety switch mounted on the frame of the planing device. When engaged the safety switch allows current flow through a conductive planing element of selected resistance so that the element heats. Current flows from the planing element to the frame and handles of the planing device and to earth ground through another leg of the power cord so that at any time the device is in use an operator is protected from electrical shock.
The planing element is mounted between two tension arms which maintain such tension in the planing element that it is able to slice through a heat shearable workpiece while maintaining the configuration of a line segment. A pair of guide arms capable of following the general surface of the workpiece also serve as mounts for the tension arms which in turn serve as mounts for the planing element so that the planing element normally operates in the same general plane as the surface of the workpiece. Offsetting arms, one for each guide arm, provide a means of offsetting the frame upward from the surface of the workpiece so that a handle mounted to the frame rests a comfortable working distance from the surface of the workpiece. One configuration utilizes an adjustable frame to allow variation in the length of the planing element.
The advantages and further aspects of the present invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.